Search

MgO features lower dielectric constant and smaller dielectric loss tangent than LaAlO3 making it more suitable for the preparation of high-quality c-axis oriented Tl2Va2CaCuOdelta thin films for high frequency applications. The thin films were annealed in a gold gasket-sealed alumina capsule. Results reveal that the structural properties of the thin films may be improved through the preannealing of the pellets for Tl compensation.

Anisotropic Tl2Ba2CaCusOx thin films on MgO substrates were used to fabricate superconductor-normal conductor-superconductor-type step-edge Josephson junctions and superconductor-insulator-superconductor intrinsic stacked Josephson junctions. The normal resistance of the junctions were controlled to enhance their applicability to millimeter wave receivers. A fundamental mixing efficient intermediate frequency output of up to 95 K was demonstrated.

A high-impedance microwave detector was developed using a small refrigerator. The detector was fabricated with a small microbridge from superconducting YBCO composite ceramic. Its current-voltage characteristics and microwave response to electromagnetic signals was analyzed experimentally by means of the four-probe method. Results show that the proposed detector has excelent mode detection under microwave irradiation.

High-quality c-axis oriented Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub /spl delta// thin films have been prepared on MgO, which is more suitable for high frequency applications than LaAlO/sub 3/ because of its lower dielectric constant (/spl epsi/) and smaller dielectric loss tangent (tan /spl delta/). Annealing of the thin films was carried out in an alumina capsule sealed with a gold gasket. It was revealed that preannealing of the pellets for Tl compensation is effective in improving the structural properties of the thin films. X-ray diffraction (XRD) rocking curve scans of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub /spl delta// (0 0 12) reflection revealed that a full width of half maximum (FWHM) of thin films annealed with an unpreannealed pellet is 0.89/spl deg/, while that of thin films annealed with a preannealed pellet is 0.22/spl deg/. The highest critical temperature (T/sub c/) is 108 K and the highest critical current density J/sub c/ is 2/spl times/10/sup 6/ A/cm/sup 2/ at 77 K. [ABSTRACT FROM PUBLISHER]

SIS-type (Superconductor-Insulator-Superconductor) intrinsic stacked Josephson junctions (ISJJs) and SNS-type (Superconductor-Normal conductor-Superconductor) step-edge Josephson junctions (SEJJs) have been successfully fabricated using anisotropic Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub x/ thin films on MgO substrates. In order to apply them to millimeter wave receivers, their normal resistance (Rn) was controlled, which determines the impedance matching for millimeter wave signals. For electrical transport along the c-axis, the Rn of a single unit ISJJ with a 5 /spl mu/m-square mesa was estimated to be 580 /spl Omega/. For electrical transport parallel to the ab-plane, the R/sub n/ of series connected six SEJJs (6-SEJJs) with the gentle slope of 28/spl deg/ was 2.0 to 3.8 /spl Omega/. Since their responsivities as millimeter wave detectors were two to three orders of magnitude larger than those of single SEJJs, efficient IF (intermediate frequency) output of fundamental mixing with LO (local oscillation) power of a few microwatts was observed up to 95 K. [ABSTRACT FROM PUBLISHER]